Written by Alain Poupart of MiamiDolphins.comThe Dolphins have been trying to build up their running back corps over the past few years, taking a player at that position in three consecutive drafts — Daniel Thomas in 2011, Lamar Miller in 2012 and Mike Gillislee in 2013.

There’s a new face in the group this year in the form of free agent acquisition Knowshon Moreno, a first-round pick of the Broncos in 2009. Moreno joined the Dolphins after producing the first 1,000-yard season of his career and playing a significant role in helping Denver set NFL offensive records and reach the Super Bowl.

The Dolphins also signed two intriguing rookie free agents after the 2014 draft, Damien Williams and Orleans Darkwa, and find themselves with a lot of depth as training camp approaches.

RETURNING PLAYERS

• Mike Gillislee (5-11, 208) -- Gillislee is hoping to get more chances in 2014 after his rookie season was spent mostly watching and learning. Gillislee was inactive for 12 of the 16 games in 2013 and didn’t play in another. In fact, his six carries all came in the victory against the Jets at MetLife Stadium when he gained 21 yards with a long of 6 yards. Gillislee will need to impress coaches this summer to earn more playing time.

• Lamar Miller (5-10, 218) — Miller earned the starting job last season and showed flashes while finishing with 709 rushing yards and a 4.0 average. Miller also showed big-play ability, with a 49-yard run against Atlanta and a 41-yard gain against Cincinnati. Miller is hoping to become more consistent in his third season and also take steps in the passing game, both in picking up blitzers and catching the ball out of the backfield. Whether or not he retains his starting job, Miller should be an important player on offense.

• Marcus Thigpen (5-9, 195) -- Thigpen, whose primary role the past two seasons was as that of kick returner, spent the spring working as a wide receiver, but he’s still listed as a running back on the roster. At either spot, Thigpen has big-play ability, which he demonstrated with a 50-yard reception at New Orleans last season.

• Daniel Thomas (6-1, 233) -- Somewhat of a forgotten man among Dolphins running backs, Thomas is looking for another chance to live up to his status as a former second-round pick. Thomas did lead the Dolphins with four rushing touchdowns last season, but he’ll be looking to improve on his 3.7-yard average. This could be an important summer for Thomas, who faces a lot of competition for playing time.

VETERAN ADDITIONS

• Knowshon Moreno (5-11, 220) -- Perhaps more important than Moreno’s 1,000-yard performance on the ground in 2013 was his contribution to the Denver passing game. Not only did he catch an impressive 60 passes out of the backfield, Moreno also did a solid job picking up blitzers to give Peyton Manning additional time to pick apart defenses. Amid reports of minor knee surgery, Moreno’s status for the start of training camp is uncertain. What is clear is that he should play a big role on offense once he gets back to form.

ROOKIES OR FIRST-YEAR PLAYERS

• Orleans Darkwa (6-0, 210) -- The Dolphins have been trying to build up their running back corps over the past few years, taking a player at that position in three consecutive drafts — Daniel Thomas in 2011, Lamar Miller in 2012 and Mike Gillislee in 2013.

There’s a new face in the group this year in the form of free agent acquisition Knowshon Moreno, a first-round pick of the Broncos in 2009. Moreno joined the Dolphins after producing the first 1,000-yard season of his career and playing a significant role in helping Denver set NFL offensive records and reach the Super Bowl.

The Dolphins also signed two intriguing rookie free agents after the 2014 draft, Damien Williams and Orleans Darkwa, and find themselves with a lot of depth as training camp approaches.